This section introduces aspects that may help facilitate a better understanding of the disclosure. Accordingly, these statements are to be read in this light and are not to be understood as admissions about what is or is not prior art.
There are millions of individuals in the U.S. who currently experience walking disabilities frequently as a result of spinal cord and brain injuries such as stroke. The prevalence of spinal cord and brain injuries is expected to increase in the future due to the increasing aging population. Although medical care for spinal cord and brain injuries has been improving and death rates have been decreasing, many survivors still remain disabled. Walking disability remains the most frequent impairment resulting from spinal cord and brain injuries. Healthcare research has provided strong evidence that many survivors of spinal cord and brain injuries can benefit from performing repetitive gait rehabilitation training.
In addition, there are situations in which an athlete or a hobbyist desires to improve their skills in various sports or activities, e.g., a skier wishes to improve her skills on the ski slope but indoors. In such situations, a system that can assist in simulating the respective environment, e.g., skiing down a slope, can be beneficial.
While subjects with walking disabilities caused by spinal cord and brain injuries can benefit from repetitive gait rehabilitation training (or athletes and gaming enthusiasts benefiting from a training program or entertainment system), translating this concept to practice is frequently challenging. During such a training, the functionally-impaired leg or legs are not capable of fully supporting the entire body weight of the subject, especially at the early stage of the gait training process when the legs are not yet sufficiently strong to support a subject's full body weight. Similarly, it is difficult to introduce force input to an athlete's entire torso and legs or to a gaming enthusiast. To overcome this challenge, researchers and rehabilitation professionals have developed various body weight support (BWS) systems to reduce the subject's body weight, so that s/he can still walk, even with functionally-impaired legs. The primary function of a BWS system is to reduce the body weight of the subject so that he or she can walk with disabled legs during training without the burden of carrying the entire body-weight.
BWS systems are commonly found as cable-suspended BWS systems. The most commonly used approach for reducing subject's body weight is to use a cable suspended in the vertical direction, as shown in FIG. 6. The cable can be controlled either passively by connecting to a counter weight or actively by connecting to an actuator. For a cable-suspended passive BWS system, the subject's body is usually suspended by a counter weight using a cable passing through a pulley. A desirable feature of such a system would be that the subject would sense a reduced weight equal to the counter weight; however, such a cable suspended passive counter-weight mechanism has drawbacks from a dynamics point of view. For example, in an ascending phase, the subject with a body weight of mp will feel a larger weight than expected due to the relative weightlessness of the counter weight (mw). In particular, if the upward acceleration of the subject's body (ap) is larger than gravity (g), the subject will feel all his or her own weight as if there is no counter weight, because the cable becomes slack (i.e., no tension) in this case. In the descending phase, the counter-weight balance system will effectively balance some or all of the subject's weight. However, the system will tend to overly balance the subject's weight because of the inertia force on the counter weight. In other words, the cable-suspended counter-weight BWS system balances too much of the subject's weight in the descending phase while it balances too little in the ascending phase, as long as the subject's body has a nonzero acceleration in the vertical direction. These undesirable effects are more significant when the leg movement of the subject is irregular, which usually happens in the early stage of a gait rehabilitation training process in which the regular gait has not yet resumed. This is because an irregular movement is associated with more significant transient dynamics, and thus more inertia force on the subject. Another drawback is that the counter weight has to be manually adjusted in order to provide selective counterweights during the rehabilitations process which makes it exceptionally challenging to automatically adjust the counter weight during the actual training.
To overcome the drawbacks of cable-suspended passive BWS systems, researchers and professionals have proposed actively-controlled cable-suspended BWS systems for gait rehabilitation training. For an actively-controlled cable-suspended BWS system, the subject's body is usually suspended through a cable which is connected to an actuator. The actuator is usually designed to reel cable in and out to effectively provide body weight support in the vertical direction. In both the ascending and descending phases of walking, the cable is actively controlled to provide a perfect force in the vertical direction in order to dynamically compensate, not only part of the body weight, but also the corresponding inertia force during walking. By replacing the counter weight with an actively-controlled force (tension in the cable), an actively-controlled cable-suspended BWS system makes the subject feel having a reduced body weight equal to the prescribed amount specified by the rehabilitation health care professional.
However, current active BWS systems suffer from forces that the subject may experience in directions other than the vertical direction. For example, while the counterweight or active cable management provide counterweight in the vertical directions, such systems do not provide any assistance in the X or Y directions in a Cartesian coordinate system. These forces can result in significant amount of instability for the subject. Also, for an athlete's training program or a gaming enthusiast entertainment system, providing forces only in the vertical or Z-direction is insufficient to achieve the desired results.
Furthermore, even in available active systems, these systems are designed to provide a negative weight to counter the subject's weight. In situations where a sudden positive weight is needed, e.g., to simulate a fall, or a sudden drop, the current systems are not capable of providing such selectivity.
Therefore, there is an unmet need for a novel method and system that can provide selective positive and negative counterweight forces to a subject during gait rehabilitation and other situations.